The metal that outlived the roof
On a well-built house from the twenties or thirties, the covering was expected to be replaced eventually and the metal was not. Copper valleys, copper step flashing, copper at the chimney. A century on, that metal is frequently in better condition than anything around it.
- 1 The ridge. The highest course, and on slate the one most often reset by hand.
- 2 The field. Slate on the older stock, shingle on the rest. Two very different clocks.
- 3 Valleys. Where leaf litter settles, and where a slate roof usually ends its life.
- 4 Wall flashing. The party wall of a row or twin, rising through a roof two houses share.
- 5 Penetrations. Holes cut on purpose. When access is awkward they get sealed instead of rebuilt.
- 6 The overhang. Where meltwater from a warm attic reaches cold framing and stops.
Why it lasts
Copper develops a stable surface and then stops changing. It does not rust through the way plated steel does, and where it was installed at a decent gauge and properly formed rather than merely folded, it can outlive two coverings.
The failure mode, when it comes, is rarely the metal itself. It is the fastening and the joints: nails that worked loose, solder that fatigued, a valley that was walked on and creased.
The decision at replacement time
A fast tear-off treats all metal as debris. That is efficient, and on a house with ordinary galvanised flashing it is correct. On a house with sound copper it is a real loss: the replacement metal will not be copper unless someone pays for it, and the price difference is significant.
The alternative is to keep and reset what is sound, and replace only what is not. It takes longer, it requires someone who can work the metal rather than just remove it, and it should appear in the quote as a decision rather than an assumption.
How to know what you have
From the ground, look into the valleys and at the chimney after a rain. Copper reads brown or green rather than silver, and it will not show the streaked rust that failing steel does. If it is there, say so when you ask for quotes, because it changes what a competent contractor proposes.